# Surf for More Math

## CHAPTER 3: ADDITION AND SUBTRACTION STRATEGIES

**Lesson 7: Using Mental Math to Subtract **

Use these interactive activities to encourage students to have fun on the Web while learning about using mental math strategies to subtract 2-digit numbers. Students can try these activities on their own or in pairs.

**Goal**

Subtract 2-digit numbers by subtracting tens and then adding or subtracting ones.

**Builds Upon**

Student Book pages 72–73

**Instructions for Use**

Ghost Blasters (Subtraction) has students solve 2-digit subtraction problems by choosing the correct answer. Note that this is a two-player game.

After reading the instructions, click “Next.” Enter both players’ names in the boxes, then click “Begin.” Read the subtraction problem at the bottom of the screen, then click on the ghost that contains the correct answer. Note that the player who is supposed to answer each question is shown in red below the subtraction problem.

Mystery Picture has students use mental math strategies to solve subtraction problems.

Wait for the UFOs to appear on screen. Once the UFOs have appeared, select a UFO at the right, then click on the number in the square at the left that is the answer to the problem on the UFO. If your answer is correct, the square will reveal part of the mystery picture.